A significant field of application for friction linings is that of vehicles, in particular motor vehicles, rail vehicles, and aircraft. However, friction linings are also used in mechanical equipment.
Known friction linings, which can also be called friction lining mixtures, include reinforcement fibers such as glass, aramide, PAN, viscose; fillings materials, such as heavy spar, kaolin, or mica; metals in the form of powder, cuttings, or wires; and slip agents or solid lubricants such as antimony sulfide, molybdenum sulfide, or graphite. These components are connected by at least one organic binding agent, such as phenol resins, and types of rubber, such as SBR or NBR. For wet-prepared friction material masses, aqueous and solvent-containing resols are also used.
It is common to all the applications of friction linings that the adhesion factor or coefficient of friction is stable over as wide a range of temperatures as possible. Furthermore, the countermaterial of the counterpiece, e.g., a cast iron brake disk or pressure plate in a clutch, should be as non-corrosive as possible and itself be wear-resistant. Stability of form at high temperatures is also important.
It has already been attempted to meet the product-specific demands on friction linings, in particular by the choice of the binding agent, where, for example, with the use of novolak-hexamethylene tetramine powdered resin the novolak base was physically and chemically modified or the cross-link density of the material was influenced by different hexamethylene tetramine content of the powdered resin. In so doing, there was an effect on temperature stability, in particular in modifications with phosphorous, boron, and silicon compounds (Kunststoffhandbuch, Handbook of Plastics, Volume 10 (duroplasts), published by Prof. Dr. Wilbrand Woebcken, 2nd Edition 1998, Carl Hanser Verlag, Munich, Vienna, ISBN 3-446-14418-8).
Nevertheless, when using organically bound friction linings with a high thermal load the organic components are still always subject to decomposition reactions which have as a consequence wear and fading effects. In this connection it is to be taken into account that, e.g., in brake disks, temperature peaks up to 1000° C. can occur. Due to growing motor powers, vehicle weights, and new technologies such as, for example, double-clutch transmissions, greater and greater demands with regard to temperature stability or thermostability are being placed on friction linings.